Rionach Sayre was the mother of Ilvermorny founder Isolt Sayre. She was a Pure-blood Irish witch descended from Salazar Slytherin through the line of Gaunt. Her husband William Sayre was also a Pure-blood descended from the famous witch Morrigan, but the couple was friendly with Muggles and raised their daughter to ignore blood status. Rionach’s estranged sister Gormlaith Gaunt strongly disapproved of their attitudes toward Muggles, so Gormlaith put a stop to it by killing Rionach and William in a fiery attack on their cottage and taking Isolt back to Hag’s Glen (Pm:Ilvermorny).
Rionach owned a gold brooch shaped like a Gordian Knot. It fell into Gormlaith's possession until Isolt stole it and escaped from her aunt. Isolt later incorporated symbols of the brooch into her school (Pm).
Isolt and James's daughter Rionach Steward was named for her grandmother (Pm).
Rionach and her sister Gormlaith are related to the English Gaunt family.
Produced magical cures for her Muggle neighbors and their animals (Pm).